Limaprost reduces motor disturbances by increasing the production of insulin-like growth factor I in rats subjected to spinal cord injury

Abstract

Calcitonin gene-related peptide (CGRP) released from sensory neurons increases the production of a neuroprotective substance insulin-like growth factor I (IGF-I), and sensory neuron stimulation contributes to a reduction of spinal cord injury (SCI) by inhibiting inflammatory responses in rats. Because receptors for prostaglandin E₂ (EP receptors) are present on sensory neurons, it is possible that prostaglandin E₁ analog limaprost reduces SCI by increasing IGF-I production through sensory neuron stimulation. We examined this possibility in rats subjected to compression-trauma-induced SCI. Limaprost increased the CGRP release from dorsal root ganglion (DRG) neurons isolated from rats, and this increase was reversed by pretreatment with the EP4 receptor antagonist ONO-AE3-208. Spinal cord tissue levels of CGRP and IGF-I were increased after the induction of SCI, peaking at 2 h postinduction. The intravenous administration of limaprost enhanced increases of spinal cord tissue levels of CGRP, IGF-I, and IGF-I mRNA at 2 h after the induction of SCI. Increases of spinal cord tissue levels of tumor necrosis factor, caspase-3, myeloperoxidase, and the number of apoptotic nerve cells were inhibited by the administration of limaprost. Motor disturbances of hind legs in animals subjected to the compression-trauma-induced SCI were reduced by the administration of limaprost. These effects of limaprost were reversed completely by pretreatment with a specific transient receptor potential vanilloid 1 inhibitor SB366791 and by sensory denervation. These observations strongly suggest that limaprost may increase the IGF-I production by stimulating sensory neurons in the spinal cord, thereby ameliorating compression-trauma-induced SCI through attenuation of inflammatory responses.